verb · to combat a harmful person or situation by using the same methods or another evil force; to fight fire with fire

警方决定以毒攻毒，派出一名改过自新的罪犯去打入犯罪集团内部。

idiom · to use poisonous substances as a medical cure for diseases caused by toxins or similar ailments in Traditional Chinese Medicine

医生尝试以毒攻毒，用微量毒素来治疗这种罕见的血液病。